The objective is to study post-receptor light-adaptation mechanisms and spatial adaptational mechanisms within chromatic pathways. Pathways will be isolated with the method of 'silent substitution' and Stiles's two-color threshold method. Two investigations will be pursued: 1. Post-receptor light-adaptation of the red (R) and green (G) cone pathways will be studied by varying the ratio of radiances of both mixed red-and-green test stimuli and mixed red-and-green uniform adapting fields. Test flashes will be simultaneous increments and decrements. The method may reveal post-receptor adaptation mechanisms whose gain is set by G and R cone interactions due to field per se. Varying the ratio of red and green test flashes on a yellow field will sensitively demonstrate interactions of G and R cone signals and show effects of incremental versus decremental chromatic flashes. Other spatial test patterns will show that spatial factors strongly control G and R cone signal interactions. 2. Spatial adaptation of the short-wavelength pathway will be measured with violet or red interference gratings on a bright yellow field. Our present work shows that spatial adaptation can be confined to the short-wavelength pathway. This orientation-specific adaptation is remarkable because it shows no interocular transfer. Further measurements will determine spatial sensitivites of channels to orientation, spatial frequency, and movement.